1. Field of the Invention
The present invention relates to a throttle controller mounted in an internal combustion engine, and more particularly to a throttle controller which controls the opening and closing of a throttle valve in response to the operation of an accelerator by means of a driving source such as a motor and which is capable of effecting various types of control such as control of constant-speed running by means of a drive controlling means.
2. Description of the Related Art
A throttle valve of an internal combustion engine is adapted to control a fuel-air mixture in a carburetor and an output of the internal combustion engine in an electronically controlled gasoline injector by adjusting the amount of air intake. The throttle valve is arranged to be interlocked with an accelerator operating mechanism including an accelerator pedal.
Although, conventionally, the accelerator operating mechanism is mechanically connected to the throttle valve, apparatus have recently been proposed for opening and closing the throttle valve in response to the operation of an accelerator by means of a driving means interlocking with a driving source such as a motor. For instance, Japanese Patent Laid-Open No. 14586/1980 discloses an apparatus in which a stepping motor is connected to a throttle valve and the stepping motor is driven in response to the operation of an accelerator pedal.
With respect to such apparatus, Japanese Patent Laid-Open No. 1539/1984 enumerates examples of conventional countermeasures against cases where an electronically controlled actuator for driving the aforementioned stepping motor has become uncontrollable. For instance, the arrangement provided is such that a throttle shaft is separated from the electronically controlled actuator by means of an electromagnetic clutch, and the throttle valve is returned to its closed position by means of a return spring. In this publication, countermeasures are provided on the grounds that no driving means are provided in the aforementioned conventional examples for opening and closing the throttle valve after control by the electronically controlled actuator is stopped, which makes it impossible to move the vehicle to a specified place for repair.
Specifically, the arrangement provided is as follows: An electromagnetic clutch is interposed between the throttle shaft and a rotating shaft which rotates as the accelerator pedal is pressed, the electromagnetic clutch being adapted to disengage the two shafts when it is excited, and couples the two shafts when not excited. Also interposed between the two shafts is a control circuit which is adapted to drive a relay upon detecting any abnormality in the control operation of the electronically controlled actuator, thereby stopping power supply to the electronically controlled actuator and the electromagnetic clutch. When the electronically controlled actuator has become uncontrollable, the throttle shaft is mechanically connected to the accelerator pedal via the electromagnetic clutch.
In the technique disclosed in the aforementioned publication of Japanese Patent Laid-Open No. 153945/1984, the uncontrollable state of the electronically controlled actuator is detected by another control circuit, and the power supply to the actuator and the electromagnetic clutch is stopped by this control circuit. It is stated in the publication that after control is stopped, the rotating shaft mechanically connected to the accelerator pedal is connected to the throttle shaft via the electromagnetic clutch. In addition, even after the operation has shifted to the operation by the accelerator pedal, the state in the accelerator pedal is still connected to the actuator is maintained, as it is explained concerning the operation of an embodiment that since drive torque is not produced in the motor in a state in which the electronically controlled actuator has stopped control, the accelerator pedal can be pressed with only a light force, and that no hindrance is therefore caused to the opening and closing of the throttle valve by the pressing of the accelerator pedal.
However, the electromagnetic clutch used in such conventional apparatus is large in size in terms of its structure, and its cost is high. In addition, it cannot be said that the possibility of not only the electronically controlled actuator becoming uncontrollable but also the aforementioned control circuits malfunctioning is nil. For instance, there is the possibility that the throttle valve continues to be driven toward the opening side owing to, for instance, radio interference or the like. In such a case, even if a switching means is provided separately, and an attempt is made to connect the throttle shaft to the accelerator pedal with the power supply to the electromagnetic clutch stopped, there is no means for actuating the throttle valve toward the closing side in opposition to the throttle shaft driven by the actuator, so that it becomes difficult to secure a desired throttle opening.
If the above-described situation has occurred, the driver generally stops the operation of the accelerator and effects a braking operation. With the above-described conventional apparatus, however, the throttle valve continues to be driven by the actuator.
For this reason, the subject applicant has disclosed in Japanese Patent Application No. 22190/1989 a throttle controller in which the driving means can be separated positively from the throttle valve and throttle control by the driving source can be stopped, when the stopping of the operation of the accelerator is detected and when it is detected that a predetermined throttle opening is exceeded then.
In the aforementioned throttle controller as well, the function of controlling running at a constant speed is required for allowing the vehicle to run at a fixed speed even if the accelerator pedal is not pressed once the vehicle speed is set to a desired speed during running of the vehicle. However, if the arrangement is provided such that the driving means is separated from the throttle valve when the throttle opening has exceeded a predetermined opening when the operation of the accelerator is stopped, as described above, the driving means is separated with the operation of the accelerator stopped during running of the vehicle. In this state, the constant speed running control becomes impossible. Accordingly, during control of constant-speed running, it is essential to allow throttle control by the driving source to continue even when the accelerator is not operated.
In addition, during running of the vehicle by constant-speed running control, the accelerator pedal is normally in an nonoperative state, and if the constant-speed running control is canceled is this state, the throttle opening becomes sharply small. Subsequently, the operation proceeds immediately to the normal accelerator control, and the driving source is driven in response to the operation of the accelerator until the throttle valve reaches a desired opening. However, drivability is impaired due to the aforementioned sharp decline in throttle opening.